Network cable

You need to worry more about lightning strikes..

Keep the wire far enough away so that if your power likes do get hit, the strike can not make it over to your network cables.

That's not to say that your devices connected to the grid won't get hit so what ever :)

At least 6 inches or more I would say for that, as for basic line noise, you can get close to the wores.

Network cables are twisted pairs so they are design to reduce external noise to a degree.

Jamie

Fire safety usually dictates circa 1 foot separation (that's because of lightning, not for normal operation). They work fine if you bundle AC and data wiring all together with a velcro strap under your desk, of course, but wires in the attic might be regarded as 'installed' in the building, and that's the recommended separation of low-voltage and power wiring runs, if there's no conduit.

I vaguely recall that NEC requires 2" separation between signal and power cables for safety. I'm not sure of the 2" and am too lazy to look it up.

If you're worried about coupling between the 60Hz power lines and the CAT5e network cable, everything depends on the distance that they run in parallel. If it's fairly short, or the cables simply cross, there's no cross coupling. However, if you're running something like

In theory, ethernet is immune to low frequency (60 Hz) interference. In reality, the power lines contain substantial amounts of higher frequency noise and junk that MIGHT couple to the ethernet cable. The common mode rejection of the twisted ethernet wires dramatically reduces coupling, but if sufficiently strong, you may have problems. For example, if you're wiring a factory full of sewing machine motors, you should certainly keep the network cables away from the power lines as the variable frequencies, high power levels, and high noise levels from these motors can cause problems.

You really should ask this question in one of the wiring newsgroups, such as comp.dcom.cabling.